Changing the shape and color of keratinous fibers, in particular hair, represents an important area of modern cosmetics. The appearance of the hair may thus be adapted to current fashion trends and to the person's individual preferences. Coloring, in particular covering up gray hair, is sought by people of all cultures. People from cultures with naturally curly hair also often seek options for straightening the hair.
Hair straightening agents are used for straightening curly hair. In this regard, the hair straightening agents must meet a number of minimum requirements: The agents must allow effective straightening of the very curly hair, in particular for the very strong curl found in African type hair, for example, wherein the straightening should take place regardless of the condition of the hair. In addition, the agents must have temperature stability, should have an optimal consistency, should not cause skin irritation, and should be capable of being easily washed out. Furthermore, the agents should not cause excessive damage to the hair. The most commonly used method of straightening very curly hair is treatment of the hair with preparations based on sodium hydroxide, potassium hydroxide, lithium hydroxide, and/or guanidinium hydroxide. When these hair straightening agents are applied, the cystine bonds present in the hair are cleaved, and approximately one-third of the cystine is converted to lanthionine. Since the hair straightening carried out using the above-mentioned hydroxides exposes the hair to strong alkalinity, damage to the hair is often not avoidable.
For changing the color of the hair, those skilled in the art are familiar with various coloring systems, depending on the requirements for the coloring. For long-lasting, intense colorations having appropriate fastness properties, so-called oxidation dyes are used. Such coloring agents customarily include oxidation dye precursors, so-called developer components and coupler components, which form the actual dyes with one another under the influence of oxidizing agents, for example hydrogen peroxide. Oxidation dyes are characterized by excellent, long-lasting color results, but are also associated with a certain degree of damage to the hair. When oxidation dyes are used in combined straightening-dyeing processes, the damage would accumulate, for which reason the use of oxidation dyes in straightening-dyeing processes is not indicated.
The hair color may be temporarily changed by using direct dyes. In the process, dyes which are already formed diffuse from the coloring agent into the hair fiber. Compared to oxidative hair coloring, the colorings obtained with direct dyes are not as durable and wash out more quickly. However, the lesser amount of damage from coloring with direct dyes is advantageous.
Methods for combined straightening and dyeing of hair have already been described in the prior art. For example, WO 2013/098335 A2 discloses a method for straightening and dyeing keratin fibers, in which hydroxide bases and dyes are simultaneously applied to the fibers. However, the methods and agents known from the prior art are often associated with a high to a very high level of damage to the hair.
It is therefore desirable to provide a low-damage method for straightening and dyeing keratinous fibers. By use of this method, the aim in particular is to allow even very curly hair, such as African type hair, for example, to be effectively straightened and dyed. The hair should preferably experience less damage due to this method.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.